Score : 300 points
There is an integer sequence A of length N whose values are unknown.
Given is an integer sequence B of length N-1 which is known to satisfy the following:
B_i \geq \max(A_i, A_{i+1})
Find the maximum possible sum of the elements of A.
Input is given from Standard Input in the following format:
N B_1 B_2 ... B_{N-1}
Print the maximum possible sum of the elements of A.
3 2 5
9
A can be, for example, ( 2 , 1 , 5 ), ( -1 , -2 , -3 ), or ( 2 , 2 , 5 ). Among those candidates, A = ( 2 , 2 , 5 ) has the maximum possible sum.
2 3
6
6 0 153 10 10 23
53